The following abbreviations used in the specification and/or the drawings are defined as follows:
CA Carrier Aggregation
CC Component Carrier
DL Downlink
DM RS Demodulation Reference Signal
eNB Enhanced Node B. Name for Node B in LTE
FFT Fast Fourier Transform
ICIC Inter-Cell Interference Control
LTE Long Term Evolution
LTE-A Long Term Evolution Advanced
MDCH Master Discovery Channel
PBCH Physical Broadcast Channel
Pcell Primary Cell
PCC Primary Cell Carrier
PDCH Physical Discovery Channel
PDCCH Physical Downlink Control Channel
P-SCH Primary Synchronisation Channel
PSS Primary Synchronisation Signal
PUSCH Physical Uplink Shared Channel
RRC Radio Resource Control
RRH Remote Radio Head
RSRP Reference Symbol Received Power
RSRQ Reference Symbol Received Quality
Scell Secondary Cell
SCC Secondary Cell Carrier
S-SCH Secondary Synchronisation Channel
SSS Secondary Synchronisation Signal
TTI Time Transmit Interval
UE User Equipment
UL Uplink
CRS Cell-specific Reference Signal
CSI-RS Channel state information Reference Signal
Of particular interest herein are the further releases of 3GPP LTE (e.g., LTE Rel-10) targeted towards future IMT-A systems, referred to herein as LTE-Advanced (LTE-A). Reference in this regard may be made to 3GPP TR 36.913, V8.0.1 (2009 03), 3rd Generation Partnership Project; Technical Specification Group 30 Radio Access Network; Requirements for Further Advancements for E-UTRA (LTE-Advanced) (Release 8). A goal of LTE-A is to provide significantly enhanced services by means of higher data rates and lower latency with reduced cost. LTE-A is directed toward extending and optimizing the 3GPP LTE Rel-8 radio access technologies to provide higher data rates at low cost.
LTE-A should operate in spectrum allocations of different sizes, including wider spectrum allocations than those of Rel-8 LTE (e.g. 10-100 MHz) to achieve the peak data rate of 100 Mbits for high mobility and 1 Gbits for low mobility. It has been agreed that Carrier Aggregation (CA) is to be considered for LTE-A in order to support bandwidths larger than 20 MHz.
CA permits an LTE base station to group several distinct channels into one logical channel, thereby aggregating two or more component carriers (CCs) and enabling very high peak traffic channel data rates.
CA in LTE-Advanced extends the maximum bandwidth in the uplink (UL) or downlink (DL) directions by aggregating multiple carriers within a frequency band (intra-band CA) or across frequency bands (inter-band CA). A primary cell carrier (PCC) using LTE technology may be configured on a LTE licensed band for primary access providing mobility, security and state management for user terminals while a secondary cell carrier (SCC) using another carrier (e.g., a carrier using WLAN technology) may be configured/activated on an un-licensed band for secondary access to provide additional data plane transport. The SCC may have one or more secondary cells (SCell) for providing radio connectivity to user terminals.
Finding a free channel in an unlicensed band can be difficult because there are many other systems that might utilize frequencies within the licensed band. Potential co-existing systems may include: IEEE 802.11 b/alg/nlac, Bluetooth, Zigbee, etc. To use the unlicensed band, the LTE systems are required to adopt agile spectrum and time sharing techniques, and user terminals must conclude time/frequency synchronisation quickly.
To that end, a physical channel referred to as a Physical Discovery Channel (PDCH) that is optimized to SCC discovery has previously been considered. The PDCH has a long periodicity, which may be a few seconds, and is considered to be suitable for SCC discovery.
However, the inventors consider the PDCH to be unsuitable for accurate time and frequency synchronisation on the SCC.
Embodiments are directed towards providing an improved method for time and frequency synchronisation in inter-band carrier aggregation.